The present invention relates to an apparatus for seismic measurements, wherein at least one seismic source and hydrophone devices are towed behind a vessel, and wherein a pair of deflectors are used that are submerged in the sea and have a means between them designed to ensure that the spacing between the hydrophone devices transverse to the vessel's direction of travel is maintained in that, as the vessel moves, the deflectors seek to move in a direction transverse to the vessel's direction of travel, a wire being fastened between the said deflectors in order to limit the spacing between the deflectors.